This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Application No. 2000-193069 filed on Jun. 27, 2000, the entire content of which is incorporated herein by reference.
The present invention generally relates to a headrest. More particularly, the present invention pertains to a vehicle seat headrest which is adjustable to vary the vertical position of the headrest.
Japanese Patent Laid-Open Publication No. H05-253034 and German Patent Publication NO. DE4407519C2 disclose known vertically adjustable headrest. These known headrests include a position adjusting device having a motor unit that flexibly adjusts the vertical position of a headrest in accordance with the head position of an occupant. The position adjusting device is accommodated in a seat backrest frame. In Japanese Patent Laid-Open Publication No. H05-253034, the motor unit is disposed on the bottom position in the backrest. In German Patent Publication No. DE4407519C2, the motor unit is positioned at one side of the upper portion in the backrest with a bracket. The motor unit is positioned to provide a rotational drive force via a deceleration gear mechanism to a geared drive shaft. The geared drive shaft is located approximately at the middle portion of the backrest and extends in the vertical direction. In German Patent Publication No. DE4407519C2, a motor and the geared drive shaft are connected with a gear cable. In Japanese Patent Laid-Open Publication No. HC5-253034, the position adjusting device is positioned at the bottom portion of the backrest at a position corresponding to the height of the knees of an occupant in the rear seat. Accordingly, the motor unit positioned at the bottom portion of the backrest enlarges the thickness of the backrest. This restricts the design needs to ensure that the interior space for the occupants is as large as possible. To avoid the aforementioned drawback, German Patent Publication No. DE4407519C2 discloses a system in which the motor unit is provided at the upper portion of the backrest on one side. However, the geared drive shaft for moving the headrest in the vertical direction is positioned at the middle of the backrest. Thus, the motor unit and the geared drive shaft are connected via a gear cable. This increases the number of components and thus the manufacturing cost.
A need thus exists for an adjustable headrest device that does not require the same amount of space in the seat backrest so that the seat backrest can be made thinner than that required for other known devices.
A need also exists for an adjustable headrest device that can be manufactured less expensively than other known devices.
According to one aspect of the invention, an adjustable headrest device includes a seat backrest including a seat backrest frame, a pair of parallel longitudinal stay shafts projecting upwardly from a top end of the seat backrest, and a position adjusting device disposed in the seat backrest. The position adjusting device includes a motor unit, a vertically extending threaded drive shaft operatively connected to the motor unit, a movable member including a nut portion engaged with the drive shaft to vertically move along the drive shaft and a stopper connecting the movable member with each of the longitudinal stay shafts, and a guide disposed parallel to the drive shaft for guiding vertical movement of the movable member, with the motor unit being positioned between the longitudinal stay shafts at the upper portion of the drive shaft.
According to another aspect of the invention, a headrest device includes an upright seat backrest frame, a headrest frame, a pair of stay shafts extending from the headrest frame, a motor unit mounted on the seat backrest frame at a position between the stay shafts and having a motor and a deceleration gear mechanism, a vertically extending threaded drive shaft having an upper portion directly engaged with the deceleration gear mechanism so that output from the motor transferred to the deceleration gear mechanism is directly transferred to the drive shaft, and a movable member threadably engaged with the drive shaft to move along the drive shaft upon operation of the motor. The movable member is provided with a pair of holes, with each of the stay shafts being positioned and secured in one of the holes of the movable member. A guide is disposed parallel to the drive shaft, with a portion of the movable member engaging the guide during movement of the movable member along the drive shaft.
According to a further aspect of the invention, an adjustable headrest device includes an upright seat backrest frame, a headrest that includes first and second stay shafts, a threaded drive shaft, a motor mounted on the seat backrest frame and operatively engaging an upper end portion of the drive shaft to rotate the drive shaft upon operation of the motor, and a movable member threadably engaged with the drive shaft to move along the drive shaft upon rotation of the drive shaft, with the first stay shaft being fixed in place to a first portion of the movable member and the second stay shaft being fixed in place to a second portion of the movable member. The drive shaft is positioned closer to the first portion of the movable member than to the second portion of the movable member. A guide is secured to the seat backrest frame and is disposed parallel to the drive shaft, with a portion of the movable member engaging the guide during movement of the movable member along the drive shaft.